Modifies the stack pointer for a less privileged access mode.
    The operating system uses this service to modify a stack pointer
    for a less privileged access mode after placing arguments on the
    stack.

    Format

      SYS$ADJSTK  [acmode] ,[adjust] ,newadr

    C Prototype

      int sys$adjstk  (unsigned int acmode, short int adjust, void

                      *(*(newadr)));